Spring Boot is a widely used framework for building Java-based enterprise applications with ease and speed. Interviewers typically focus on Spring Boot concepts, dependency injection, RESTful services, and microservices architecture. The following 25 Java Spring Boot Developer Interview Questions and Answers will help you prepare thoroughly.

Q1. What is Spring Boot?

Spring Boot is an open-source Java-based framework used to create stand-alone, production-grade Spring applications with minimal configuration.

Q2. How does Spring Boot differ from the Spring Framework?

Spring Boot simplifies Spring Framework by providing default configurations, embedded servers, and starter dependencies to reduce setup time.

Q3. What is the purpose of the @SpringBootApplication annotation?

@SpringBootApplication is a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations.

Q4. What are Spring Boot starters?

Starters are pre-configured dependency descriptors that help you add common libraries to your project easily.

Q5. What is auto-configuration in Spring Boot?

Auto-configuration automatically configures Spring applications based on the dependencies present in the classpath.

Q6. How do you create a RESTful web service in Spring Boot?

By using @RestController to define the controller and mapping HTTP requests with @GetMapping, @PostMapping, etc.

Q7. What is the use of application.properties or application.yml?

These files are used to define application configurations like database settings, server ports, and custom properties.

Q8. How does Spring Boot handle dependency injection?

Spring Boot uses the Spring Framework’s IoC container to inject dependencies via annotations like @Autowired and constructor injection.

Q9. What is the difference between @Component, @Service, and @Repository?

All are stereotypes for Spring beans, but @Service marks service layer, @Repository marks data access layer with exception translation, and @Component is a generic stereotype.

Q10. What is Spring Boot Actuator?

Actuator provides production-ready features like health checks, metrics, and monitoring for Spring Boot applications.

Q11. How do you configure a database connection in Spring Boot?

By specifying datasource properties in application.properties or application.yml and using Spring Data JPA or JDBC templates.

Q12. What is the role of @EnableAutoConfiguration?

It enables Spring Boot’s auto-configuration mechanism based on the project dependencies.

Q13. How do you implement exception handling in Spring Boot REST APIs?

By using @ControllerAdvice and @ExceptionHandler annotations to manage global and specific exceptions.

Q14. What is the difference between @RestController and @Controller?

@RestController combines @Controller and @ResponseBody, returning JSON/XML response directly, while @Controller typically returns views.

Q15. How can you secure a Spring Boot application?

By integrating Spring Security for authentication and authorization, and configuring security rules in the application.

Q16. What is the importance of profiles in Spring Boot?

Profiles allow you to define environment-specific configurations, like dev, test, or production, using different property files.

Q17. What is the purpose of the CommandLineRunner interface?

It is used to execute code after the Spring Boot application has started, often for initialization tasks.

Q18. How do you create a custom starter in Spring Boot?

By creating a reusable project with auto-configuration and packaging it as a Maven/Gradle dependency.

Q19. What is the role of Spring Boot CLI?

Spring Boot CLI allows you to quickly develop Spring applications using Groovy scripts from the command line.

Q20. How do you monitor Spring Boot applications?

Using Spring Boot Actuator endpoints, external monitoring tools, or integration with logging and metrics frameworks.

Q21. How can you run Spring Boot applications?

You can run them as standalone jar files with embedded servers, from IDEs, or using Maven/Gradle commands.

Q22. What is the difference between @Autowired and @Inject?

@Autowired is Spring’s own annotation for dependency injection; @Inject is from the Java CDI standard but works similarly in Spring.

Q23. How do you handle transactions in Spring Boot?

By using @Transactional annotation on service methods to manage transaction boundaries.

Q24. What is the use of Spring Boot DevTools?

DevTools provides features like automatic restart and live reload to improve developer productivity.

Q25. How do you test Spring Boot applications?

Using Spring Boot Test framework with annotations like @SpringBootTest, MockMvc, and Mockito for unit and integration tests.